In an email exchange with MacRumors today, an IOC spokesperson was
asked about athletes being asked to cover non-Samsung logos on
mobile devices. She responded saying the report was “not true”:

No it is not true. Athletes can use any device they wish during
the Opening Ceremony. The normal rules apply just as per
previous Games.

The Samsung Note 3 that were distributed are a gift to the
athletes, so they can capture and share their experiences at the
Games, and the phones also contain important competition and
logistical information for competing athletes.

It is possible that Samsung requested that logos be covered, but
it is not an official IOC request and athletes will not be
penalized for using or displaying non-Samsung phones.